It is known in the art to employ radar technology in exterior automotive applications, such as driver assistance systems, for providing improved safety by facilitating an optimized reaction of a driver of a vehicle with appropriate warnings, such as vulnerable road user detection systems, lane change assist systems or blind spot monitoring systems, or even by automatically taking over control of the vehicle, for instance in collision mitigation systems. The most common exterior automotive rated devices operate at radar carrier frequencies in regimes about 24 GHz or about 77 GHz.
A typical scenario is illustrated in FIG. 1. A vehicle 18 designed as a passenger car uses a radar system 10 that is installed at a front region 22 of the vehicle 18 and that transmits radar waves towards a scene in front of the vehicle 18 for detecting obstacles 24 or vehicles 20 of an oncoming traffic appearing in the radar system field of view 26 in a detection path 28. In the following, the radar wave-transmitting radar system 10 is referred to as “ego radar system” for brevity.
Moreover, there is an upcoming desire to furnish vehicles with automatic communication systems, serving the purpose of avoiding accidents and thus potential injuries. In FIG. 1, this is indicated by a communication path 30 between the ego radar system 10 and a radar system 10 of the oncoming vehicle 20 shown on the left side of FIG. 1 as a communication partner.
A fast and reliable communication could be based on electromagnetic waves, which are already generated by on-board radar systems, however, those usually are primarily designed for detection of obstacles and traffic participants, and not for communication purposes in the first place. Consequently, radar systems that also enable communication are held to require a huge amount of technical effort.
For instance, in the article by Shrawan C. Surender and Ram M. Narayanan, “UWB Noise-OFDM Netted Radar: Physical Layer Design and Analysis”, IEEE Transactions on Aerospace and Electronic Systems, vol. 47, no. 2, April 2011, pp. 1380-1400, a scheme is proposed to modify an ultra-wideband (UWB) noise radar in order to supplement it with secure multi-user network communication capabilities. UWB noise radar achieves high-resolution imaging of targets and terrain. The wide bandwidth yields fine range resolution, while the noise waveform provides immunity from detection, interference, and interception. Having multiple noise radars networked with each other provides significant benefits in target detection and recognition. The salient features of the proposed UWB noise-orthogonal frequency-division multiplexing (OFDM) multi-functional netted radar system include surveillance with embedded security-enabled OFDM-based communications, multi-user capability, and physical layer security.
In the relevant article, a single waveform has been designed by dividing the available bandwidth into three sections, wherein communication information is embedded in the center of a spectrum and two side bands are allocated for radar. The effect of communication data on target range estimation has been investigated, but the influence of the Doppler shift is not considered.
In the article by A. Hassanien, M. G. Amin, Y. D. Zhang and F. Ahmad, “Dual-Function Radar-Communications: Information Embedding Using Sidelobe Control and Waveform Diversity,” IEEE Transactions on Signal Processing, vol. 64, no. 8, Apr. 15, 2016, pp. 2168-2181, a technique for a dual-function system with joint radar and communication platforms is described. Sidelobe control of the transmit beamforming in tandem with waveform diversity enables communication links using the same pulse radar spectrum. Multiple simultaneously transmitted orthogonal waveforms are used for embedding a sequence of LB bits during each radar pulse. Two weight vectors are designed to achieve two transmit spatial power distribution patterns, which have the same main radar beam, but differ in sidelobe levels towards the intended communication receivers. Communication information is transmitted by controlling side-lobe levels of beam-pattern at fixed points in an angular space. The receiver interpretation of the bit is based on its radiated beam. The proposed technique allows information delivery to single or multiple communication directions outside the main lobe of the radar. It is shown that the communication process is inherently secure against intercept from directions other than the pre-assigned communication directions. The employed waveform diversity scheme supports a multiple-input multiple-output radar operation mode.
It is noted that stationary targets are a prerequisite of the proposed method, and a drawback is that the radar system will lose the target if it moves outside that certain angular space.
In order to eliminate this drawback, the same authors propose in the article “Phase-modulation based dual-function radar communications”, Institution of Engineering and Technology (IET) Radar Sonar Navig., vol. 10, no. 8, pp. 1411-1421, to design a bank of transmit beamforming weight vectors such that they form the same transmit power radiation patterns, whereas the phase associated with each transmit beam towards the intended communication directions belongs to a certain phase constellation. During each radar pulse, a binary sequence is mapped into one point of the constellation which, in turn, is embedded into the radar emission by selecting the transmit weight vectors associated with that constellation point. The communication receiver detects the phase of the received signal and uses it to decode the embedded binary sequence. The proposed technique allows information delivery to the intended communication receiver regardless of whether it is located in the sidelobe region or within the main radar beam. Three signaling strategies are proposed which can be used to achieve coherent communications, non-coherent communications, and non-coherent broadcasting, respectively.